Micro scale operations

Having established a high level methodology to identify intensification factors required for success, the next five sub-sections will to go through the various fundamental reaction engineering processes by means of illustrative examples and discuss differences between a mega- and a micro-scale operation. 

Distillation under reduced pressure. The student should first read details of this operation on a macro-scale (p. 28). For micro-scale work the apparatus shown in Fig. 40 is very convenient. A small pear-... 

Tausend Kandlejur eine Reaktion, Chemische Rundschau, February 2003 Industrial and institutional expert opinions general advantages of micro flow safety work of institutes particle precipitation pilot-scale operation challenges process control plugging miniature sensing and controlling emulsification market situation [204]. 

The same features were found for pilot-size micro-reactor operation (Figure 4.59). Brightness and transparency were the same and color strength could be increased to 149% [55]. The mean particle size was even set to a lower value compared with the laboratory-scale processing (micro reactor, D5Q = 90nm, s= 1.5 ... 

As a further advantage, large flows are provided by these devices, even when operating with a single device. Pilot-scale operation, with one or a few micro devices, is easily feasible. Especially in the case of foam formation, parallel operation of many devices having the same flow pattern seems to be possible. 

Conventional combustion calorimeters operate on a macro scale, that is, they require samples of 0.5-1.0 g per experiment. Unfortunately, many interesting compounds are available only in much smaller amounts. In the case of oxygen combustion calorimetry, however, several combustion microcalori-meters that only demand 2-50 mg samples have been developed in recent years. The achievements and trends in this area through 1999 have been reviewed [7-10], and interested readers are directed to these publications. Since then, a few new apparatus have been reported [11-17], Nevertheless, it should be pointed out that the general principles and techniques used to study compounds at the micro scale are not greatly different from those used in macro combustion calorimetry. 

Studies at Mobil Research have shown that light olefins instead of gasoline can be made from methanol by modifying both the ZSM-5-type MTG (Methanol-to-Gasoline) catalyst and the operating conditions. Work carried out in micro-scale fluidized-bed reactors show that methanol can be completely converted to a mixture of hydrocarbons containing about 76 wt% C2-C5 olefins. The remaining hydrocarbons are 9% C1-C5 paraffins, of which the major component is isobutane, and 15% C6+, half of which is aromatic. 

Early devices fbr thermogravimetric analysis were limited in precision and convenience when compared with DTA or DSC equipment. Now devices for simultaneous DSC and TG are on the market which can operate at high temps in reactive atms permitting the simulation of high temp reactions on a micro scale. The use of TG for the study of reaction kinetics was described in Sect 5.3.3. An exptl study of the sublimation of ammonium perchlorate was published by Jacobs and Jones (Ref 25). Similar techniques should find application in the study of other propint systems. The product gases have been collected for further analysis using gas chromatography and mass spectrometry... 

Then, a survey of micro reactors for heterogeneous catalyst screening introduces the technological methods used for screening. The description of microstructured reactors will be supplemented by other, conventional small-scale equipment such as mini-batch and fixed-bed reactors and small monoliths. For each of these reactors, exemplary applications will be given in order to demonstrate the properties of small-scale operation. Among a number of examples, methane oxidation as a sample reaction will be considered in detail. In a detailed case study, some intrinsic theoretical aspects of micro devices are discussed with respect to reactor design and experimental evaluation under the transient mode of reactor operation. It will be shown that, as soon as fluid dynamic information is added to the pure experimental data, more complex aspects of catalysis are derivable from overall conversion data, such as the intrinsic reaction kinetics. 

Owing to the small size of micro devices, new design methods are required. Similar to conventional unit operations, micro-scale pendants exist, named micro unit... 

In the above-described pChemTec project, a combination of miniplant and micro structured reactor plant equipment is used for the organoborane synthesis as an example for a future production facility for fine chemicals. This approach differs from the usual application of a miniplant as a mediator between laboratory-scale and pilot plant-scale operation. The microstructured reactor plant shown in Figure 4.47, a combination with a typical miniplant set-up, exhibits greater complexity than the miniplant but it nevertheless consumes a much smaller proportion of the volume of the plant set-up. 

As a more critical example concerning the transfer of macroscopic modeling to micro-scale applications, the following example of a simulation of a homogeneous catalytic reaction is described [133], This example also represents a typical approach in process simulation if a new reactor model or a model for a new unit operation... 

The preparation of a derivative of a sample compound prior to GC is a significant potential source of both qualitative and, in particular, quantitative errors. Almost all reactions that are used for derivatization are organic syntheses adapted to the micro-scale. This approach makes full use of an advantageous property of GC, namely the need to take only very small amounts of the sample for the analysis, but on the other hand, it makes heavy demands on the quality of the materials used and the precision of the operating procedures. As GC has especially been used in analyses of complex mixtures with large contents of various components, such as biological samples, the operations necessary for the preliminary separation of the compounds of interest from the sample, e.g., extraction or TLC, are often involved in the entire procedure, and make it even more complicated. With some reactions, the necessity for an anhydrous medium requires the application of drying (lyophilization) in the treatment of the sample. 

The present Monte Carlo Simulation technique operates employing micro scale properties such as diffusion coefficient of Lithium ions... 

For the experiments in this study, three types of reactor system were used. One had some separate micro-scale reactors, and it was used to measure HDS and HDM activity at constant operational conditions. The volume of each micro-reactor was 70 cc. 

Experimental work in a micro scale activity test equipment was performed to derive a testing strategy for the optimization of FCC unit operation due to coke deposition on catalyst. The cracking of cumene over a super-D zeolite catalyst was chosen as the model reaction because the nature of this reaction can represent the cracking of typical commercial FCC feeds such as gas-oils via the dealkylation of branched aromatics. In addition, this reaction can also eliminate any obscurity in catalyst deactivation from other contaminants. 

Pardhanani, A.L. and Carey, G.F. (2000) Multidimensional Semiconductor Device and Micro-scale Thermal Modeling Using the PROPHET Simulator with Dial-an-Operator Framework. Comput. Model. Eng. Sci., 1, 141-150. 

Scaling up of the processes to large surface areas (i.e. to obtain asymmetric membrane systems with several layers) as is necessary for large-scale operations has been successfully demonstrated for micro/ultrafiltration and bioseparation processes, but not for other applications such as gas/vapour separation and membrane reactors, for which only small-scale laboratory equipment is available. 

This problem is due to the fact that stirring experiments are generally carried out in small laboratory devices (D < 1 m), in which the micro-scale turbulence is predominant. They therefore often do not supply reliable information on scale-up for that mixing operation in which macro-scale turbulence is essential. The latter is... 

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